This invention relates to a method and apparatus for separating two immiscible liquids, for example, kitchen effluent comprised of a mixture of grease and water.
Kitchen effluent generated during food processing is normally collected in a grease trap separator, which is commonly a rectangular tank made of precast concrete, buried below grade. In the separator, the grease, being of a lower density than the water, rises to the top, forming a separate grease mat layer. Periodically, the grease is removed from the trap, normally with a vacuum pump. The grease may then be disposed of in a landfill or sold to processors, or rendering companies, for conversion into useful products.
Processing of the grease into useful products is obviously preferred to dumping of the grease into a landfill, which also may not be possible due to increased environmental regulations. Processors, however, are not always willing to accept grease if it includes a significant percentage of water, i.e., more than 15%, because of the increased difficulty in processing. Moreover, the prolonged contact of water with the grease tends to make the grease rancid as a result of the break down of lipids into shorter chain fatty acids, thus decreasing the value of the grease.
The prior art discloses various methods and apparatus for separating two immiscible liquids, and also discloses various methods and apparatus for removing one liquid from contact with the other after separation of the liquids into two layers in a separator. For example, in some cases, the lighter liquid is discharged by gravity from the separator through an upper pipe and the heavier liquid is discharged from the separator through a lower pipe. Generally, the methods and apparatus relate to the separation of grease or oil from water.
U.S. Pat. No. 2,747,736 to Mobley describes a device for removing grease from waste water in a separator, in which grease which floats to the top of the separator is removed by hydrostatic forces. The grease is then stored at a collecting and storage point remote from the separator.
U.S. Pat. No. 5,236,585 to Fink describes an apparatus comprised of a separator in which oil and water are separated. The oil, which floats to the top of the water, flows under gravity to a second separator, where remaining oil is removed, e.g., by filtration. Water is removed from the bottom of the first separator.
Other patents show similar devices. U.S. Pat. No. 4,915,823 to Hall, describes a device for separating oil from water in bilge discharges. After separation, the oil and water are removed through separate discharge pipes. U.S. Pat. No. 4,119,541 to Makaya, discloses a similar arrangement for cleaning up oil spills by separating oil from sea water. U.S. Pat. No. 4,400,274 to Protos, describes a gravity separator in which solids are removed prior to separation of the grease and water.